1. Field of the Invention
The present invention relates to a structure for inspecting the alignment of a mounted electrical component (hereinafter, referred to as a structure for inspecting the electrical component alignment), which is suitable for use in printed circuit boards used in various electronic devices.
2. Description of the Related Art
Referring to FIGS. 5 and 6, a known structure for inspecting the electrical component alignment will now be described. A planar insulated substrate 31 constituting a printed circuit board has a wiring pattern 34 having a first wiring pattern 32 and a second wiring pattern 33 both formed thereon, and an insulating resist layer 35 formed thereon so as to cover the wiring pattern 34.
The first wiring pattern 32 has a plurality of connections 32a formed by partially removing the resist layer 35.
An electrical component 36 has a rectangular outer casing 36a and a plurality of electrodes (not shown) mounted on the bottom surface of the outer casing 36a. 
Mounting of the electrical component 36 on the printed circuit board is performed by applying solder cream (not shown) on the connections 32a of the first wiring pattern 32, placing the electrodes on the solder cream, and heating the printing circuit board in a furnace so as to solder the electrodes to the connections 32a in that order.
Surface mounting of the electrical component 36 is achieved by performing reflow soldering as described above. Alternatively, the electrodes can be soldered to the connections 32a in a state such that a ball grid array having metal balls adheres to the electrodes in this soldering process.
The first wiring pattern 32 is formed for mounting and wiring the electrical component 36. The second wiring pattern 33 is additionally formed for a desired electrical circuit.
Fiducial marks 37 are formed on the resist layer 35 by silk-screen printing. More particularly, the fiducial marks 37 are formed as an L-shape at a pair of orthogonally opposing corners of the outer casing 36a of the electrical component 36 along the edges of the rectangular outer casing 36a. 
The fiducial marks 37 are formed on the resist layer 35 before mounting the electrical component 36. After the electrical component 36 is mounted, visual inspection of the fiducial marks 37 is performed to determine whether or not the electrical component 36 is aligned properly relative to the fiducial marks 37.
Since the fiducial marks 37 are formed on the resist layer 35 by silk-screen printing, the known structure for inspecting the electrical component alignment requires an additional step of silk-screen printing, thereby resulting in lower productivity and higher production cost.
Accordingly, it is an object of the present invention to provide a more productive and less expensive structure for inspecting the electrical component alignment.
To this end, a structure for inspecting the alignment of a mounted electrical component is provided. The structure comprises a printed circuit board having a wiring pattern and a rectangular electrical component mounted on the printed circuit board. The wiring pattern has fiducial portions extending closely along at least two mutually orthogonal outer edges of the rectangular electrical component.
The electrical component is preferably formed as a chip type comprising a rectangular outer casing and a plurality of electrodes mounted on the bottom surface of the outer casing.
The wiring pattern may further have a first wiring pattern which forms the fiducial portions extending along at least two mutually orthogonal outer edges of the electrical component.
The fiducial portions may further extend along the three or four outer edges of the electrical component.
The wiring pattern may further have a first wiring pattern for mounting the electrical component and a second wiring pattern which forms the fiducial portions extending along at least two mutually orthogonal outer edges of the electrical component.
The fiducial portions may further extend along the three or four outer edges of the electrical component.
The wiring pattern may further have a first wiring pattern for mounting the electrical component and a second wiring pattern so that the first wiring pattern and the second wiring pattern form the fiducial portions extending along at least two mutually orthogonal outer edges of the electrical component.
The structure for inspecting the alignment of a mounted electrical component may further comprise an insulating resist layer, which covers the fiducial portions, on the printed circuit board, wherein the fiducial portions are visible through the resist layer.